/Engine/Source/Runtime/UMG/Public/Components/CanvasPanelSlot.h
Called by the designer when a design-time widget is dragged. Returns true if the drag had any effect, false otherwise.
virtual bool DragDropPreviewByDesigner ( const FVector2D & LocalCursorPosition, const [TOptional](API\Runtime\Core\IO\TOptional)< int32 > & XGridSnapSize, const [TOptional](API\Runtime\Core\IO\TOptional)< int32 > & YGridSnapSize )